As a technology for recording and reproducing digital data, there is known a data-recording technology for using optical disks including magneto-optical disks as recording media. Examples of the optical disks are a CD (Compact Disk), an MD (Mini-Disk) and a DVD (Digital Versatile Disk). The optical disk is the generic name of recording media, which is a metallic thin plate protected by plastic. When a laser beam is radiated to the optical disk, the optical disk emits a reflected signal, from which changes can be read out as changes representing information recorded on the disk.
The optical disks can be classified into a read-only category including a CD, a CD-ROM and a DVD-ROM, which the user is already familiar with, and a writable category allowing data to be written therein as is generally known. The writable category includes an MD, a CD-R, a CD-RW, a DVD-R, a DVD−RW, a DVD+RW and a DVD-RAM. By adopting a magneto-optical recording method, a phase-change recording-method or a pigmented-coat change recording-method for the writable category, data can be recorded onto a disk of this category. The pigmented-coat change recording-method is also referred to as a write-once recording-method. Since this pigmented-coat change recording-method allows data recording once and inhibits renewal of data onto the disk, the disk is good for data-saving applications or the like. On the other hand, the magneto-optical recording method and the phase-change recording-method are adopted in a variety of applications allowing renewal of data. The applications allowing renewal of data include mainly an application of recording various kinds of content data including musical data, movies, games and application programs.
In addition, in recent years, a high-density optical disk called a blue-ray disc has been developed in an effort to produce the product on a very large scale.
Typically, data is recorded onto a high-density optical disk and read out from the disk under a condition requiring a combination of a laser with a wavelength of 405 nm and an objective lens with an NA of 0.85 to be reproduced. The laser required in this condition is the so-called blue laser. With the optical disk having a track pitch of 0.32 μm, a line density of 0.12 μm/bit, a formatting efficiency of about 82% and a diameter of 12 cm, data of the amount of up to 23.3 GB (gigabytes) can be recorded onto and reproduced from the disk in recording/reproduction units, which are each a data block of 64 KB (kilobytes).
There are also two types of optical disk having such a high density, i.e., optical disks of a write-once type and optical disks of a writable type.
In an operation to record data onto an optical disk allowing data to be recorded therein by adoption of the magneto-optical recording method, the pigmented-coat change recording-method or the phase-change recording-method, guide means for tracking data tracks is required. Thus, a groove is created in advance to serve as a pregroove. The groove or a land is used as a data track. A land is a member having a shape resembling a section plateau between two adjacent grooves.
In addition, it is also necessary to record addresses so that data can be recorded at a predetermined location indicated by an address as a location on a data track. Such addresses are recorded on grooves by wobbling the grooves in some cases.
That is to say, a track for recording data is created in advance as typically a pregroove. In this case, addresses are recorded by wobbling the side walls of the pregroove.
By recording addresses in this way, an address can be fetched from wobbling information conveyed by a reflected light beam. Thus, data can be recorded at a predetermined location and reproduced from a predetermined location without creating for example pit data showing an address or the like in advance on the track.
By adding addresses as a wobbling groove, it is not necessary to discretely provide an address area or the like on tracks as an area for recording typically pit data representing addresses. Since such an address area is not required, the capacity for storing actual data is increased by a quantity proportional to the eliminated address area.
It is to be noted that absolute-time (address) information implemented by a groove wobbled as described above is called an ATIP (Absolute Time In Pregroove) or an ADIP (Address in Pregroove).
In addition, in the case of recording media usable as media for recording these kinds of data or not as reproduction-only media, there is known a technology for changing a data-recording location on the disk by providing an alternate area. That is to say, this technology is a defect management technology whereby an alternate recording-area is provided so that, if a location improper for recording data exits on the disk due to a defect such as an injury on the disk, the alternate recording-area can be used as an area serving as a substitute for the defective location to allow proper recording and reproduction operations to be carried out properly.
The defect management technology is disclosed in documents including Japanese Unexamined Patent Publication No. 2002-521786, and Japanese Patent Laid-open Nos. Sho 60-74020 and Hei 11-39801.
In the case of a recordable optical recording medium, data cannot of course be recorded into an area in which data has already been recorded.
Specifications of most file systems to be recorded on an optical recording medium are defined by assuming the use of the optical recording medium as a ROM-type disk or a RAM-type disk. The ROM-type disk is a reproduction-only medium and the RAM-type disk is a writable optical disk. Specifications of a file system for a write-once recording medium allowing data to be stored therein only once limit functions of the ordinary file system and include special functions.
The specifications of a file system for a write-once recording medium are a reason why the file system does not become widely popular. On the other hand, a FAT file system capable of keeping up with a variety of OSes of an information-processing apparatus and other file systems cannot be applied to write-once media as they are.
Write-once media is widely used typically in applications of preserving data. If the write-once media can also be used for the FAT file system by keeping the general specifications of the file system as they are, the usability of the write-once media can be further enhanced.
In order to allow a widely used file system such as the FAT file system and a file system for RAMs or hard disks to be applied to write-once media as it is, however, a function to write data into the same address as that of existing data is required. That is to say, a capability of renewing data is required. Of course, one of characteristics of the write-once media is that data cannot be written onto the media for the second time. Thus, it is impossible to use a file system for such a writable recording medium as it is in the first place.
In addition, when the optical disk is mounted on a disk drive or dismounted from it, the recording face of the disk may be injured in dependence on the state in which the disk is kept in the drive and the way in which the disk is used. For this reason, the aforementioned technique of managing defects has been proposed. Of course, even the write-once media must be capable of coping with a defect caused by an injury.
In addition, in the case of the conventional write-once optical disk, data is recorded in a state of being compacted sequentially in areas starting from the inner side. To put it in detail, there is no space left between an area already including recorded data and an area in which data is to be recorded next. This is because the conventional disk is developed with a ROM-type disk used as a base so that, if an unrecorded area exists, a reproduction operation cannot be carried out. Such a situation limits the freedom of a random-access operation carried out on the write-once media.
In addition, for a disk drive or a recording/reproduction apparatus, an operation requested by a host computer to write data at an address specified in the operation as an address in a write-once optical disk or an operation to read out data from such an address is a process of a heavy load.
From what is described above, contemporary write-once media or, in particular, write-once media implemented by a high-density optical disk having a recording capacity of at least 20 GB like the aforementioned blue-ray disk, is required to meet the following requirements. The write-once media shall be capable of renewing data and managing defects by execution of proper management, improving the random accessibility, reducing the processing load borne by the recording/reproduction apparatus, keeping up with a general-purpose file system by the capability of renewing data and maintaining compatibility with writable optical disks as well as reproduction-only disks.